Porphyrins and bile pigments from brominated pyrromethenes
Aetioporphyrin-I (1a) is obtained in 50-60% yield by heating 5-bromo-3,4′-diethyl-3′,4,5′-trimethylpyrromethene perbromide (4a) under reflux in formic acid, surpassing the yields from the established syntheses using the less accessible 5-bromo-5′-bromomethylpyrromethene hydrobromides (2a, b). The 5-bromo-5′-methylpyrromethene hydrobromides and one equivalent of free bromine can be used as an alternative to the crystalline perbromides; in this way a 50% yield of coproporphyrin-I tetramethyl ester (1b) has been obtained. Aetiobiliverdin-IVγ (7a) is shown to be a by-product of the aetioporphyrin-I syntheses when 98% formic acid is used as the reaction medium, and the procedure has been modified to give preparatively acceptable yields of this bile pigment.
Publication Source (Journal or Book title)
Journal of the Chemical Society, Perkin Transactions 1
Smith, K. (1972). Porphyrins and bile pigments from brominated pyrromethenes. Journal of the Chemical Society, Perkin Transactions 1, 1471-1475. https://doi.org/10.1039/P19720001471